One way of tackling the question of whether human-induced climate change is now clearly detectable, is by looking to the history of climate, and asking if the surface of the planet is now warmer than it has been in past centuries.
This issue has been the subject of acrimonious debate over the last 15 years, both scientific and political. It has focused, in particular, on temperature reconstructions by Mann and others which appeared to show that the climate is now warmer, and is heating up faster, than at any time in the last 1,000 years. Their “Hockey Stick” graph has been both iconic and controversial, with critics attacking the scientific methods used and the conclusions drawn. Debates have been polarised partly because they have been politicised (especially in the US), at times “dirty” (e.g. ClimateGate) and because they have involved rival blogs which do not seek out scientific consensus. I will review the history of the debate, ask how far climate scientists should be responsive to critics outside their community and assess the difficulties of defining the limits to scientific (un)certainty.
Wikipedia's comprehensive overview of The Hockey Stick Controversy, part of the ongoing debate on climate change.
Neil is Professor of Physical Geography in Plymouth University's School of Geography, Earth and Environmental Sciences. His research interests include Holocene environmental change, diatom and stable isotope analysis and palaeolimnology (reconstruction of past in-land water environments).